Read this story from the Vancouver Sun on the recent discovery of a disease fatal to fish in Atlantic farmed salmon in Clayoquot Sound. (May 16, 2012)

For the first time in nine years Atlantic salmon farmed in British Columbian waters have tested positive for a virus that can be rapidly fatal to them, but is endemic in wild Pacific salmon and largely a low risk.

Mainstream Canada announced today that fish at its Dixon Bay farm north of Tofino tested positive for Infectious Hematopoietic Necrosis (IHN). The virus is harmless to humans, but attacks the kidneys and spleen of salmon and can lead to rotting flesh and organ failure. IHN has been present in the waters of B.C. for hundreds of years and wild salmon have developed a resistance to it, though young salmon and sockeye can be vulnerable to it, according to fish virologist James Winton.

The Canadian Food Inspection Agency will arrive at the farm tomorrow for testing as Mainstream waits to see if and how many of the roughly 500,000 farmed fish on site will have to be culled.

“This year now turns out to be a very bad year for IHN virus and we still don’t completely understand why,” said Winton, on the phone from Seattle where he works for the U.S. Geological Survey. “A lot of the sockeye were coming back with higher percentages and higher amounts of the virus, so it’s not surprising that we’re seeing a cycle again in some of the farms.

“Atlantics – they haven’t evolved with this virus so they’re sort of susceptible to all strains of [IHN].”

Mainstream spokeswoman Laurie Jensen said the virus may have been passed on to the contained salmon by a wild fish species passing through the area and that IHN is “a fact of farming and husbandry.”

Mainstream operates 27 farms in B.C., and 17 of those in the Tofino area. Those 17 are conducting IHN tests of their fish Jensen said.

If IHN is discovered, a company must call in the CFIA as well as Fisheries and Oceans Canada.